Our objective is to examine the regulatory mechanisms in the release of acetylcholine (ACh) from synaptosomal preparations. Using cortical synaptosomes that are preincubated with (methyl-3H) choline in order to synthesize labelled ACh, we will continue to explore the role of Na-K ATPase in effecting the release of the transmitter. Also, we have recently synthesized an analog of choline where antimony has replaced the nitrogen atom and will use this analog to investigate the in situ localization of ACh both in nerve terminals and in cholinergic neurons using x-ray microanalysis coupled with a scanning electron microscope. Finally, we plan to prepare plasma membrane vesicles containing ACh from synaptosomes in order to determine if the transmitter can be released in a calcium-dependent manner from a preparation devoid of synaptic vesicles.